/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.hadoop.hbase.procedure2;

import org.apache.yetus.audience.InterfaceAudience;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.hbase.thirdparty.com.google.common.annotations.VisibleForTesting;

/**
 * Basic ProcedureEvent that contains an "object", which can be a description or a reference to the
 * resource to wait on, and a queue for suspended procedures.
 */
@InterfaceAudience.Private
public class ProcedureEvent<T> {
    private static final Logger LOG = LoggerFactory.getLogger(ProcedureEvent.class);

    private final T object;
    private boolean ready = false;
    private ProcedureDeque suspendedProcedures = new ProcedureDeque();

    public ProcedureEvent(final T object) {
        this.object = object;
    }

    public synchronized boolean isReady() {
        return ready;
    }

    /**
     * @return true if event is not ready and adds procedure to suspended queue, else returns false.
     */
    public synchronized boolean suspendIfNotReady(Procedure proc) {
        if(!ready) {
            suspendedProcedures.addLast(proc);
        }
        return !ready;
    }

    /**
     * Mark the event as not ready.
     */
    public synchronized void suspend() {
        ready = false;
        if(LOG.isTraceEnabled()) {
            LOG.trace("Suspend " + toString());
        }
    }

    /**
     * Wakes up the suspended procedures by pushing them back into scheduler queues and sets the
     * event as ready.
     * See {@link #wakeInternal(AbstractProcedureScheduler)} for why this is not synchronized.
     */
    public void wake(AbstractProcedureScheduler procedureScheduler) {
        procedureScheduler.wakeEvents(new ProcedureEvent[]{this});
    }

    /**
     * Wakes up the suspended procedures only if the given {@code proc} is waiting on this event.
     * <p/>
     * Mainly used by region assignment to reject stale OpenRegionProcedure/CloseRegionProcedure. Use
     * with caution as it will cause performance issue if there are lots of procedures waiting on the
     * event.
     */
    public synchronized boolean wakeIfSuspended(AbstractProcedureScheduler procedureScheduler, Procedure<?> proc) {
        if(suspendedProcedures.stream().anyMatch(p -> p.getProcId() == proc.getProcId())) {
            wake(procedureScheduler);
            return true;
        }
        return false;
    }

    /**
     * Wakes up all the given events and puts the procedures waiting on them back into
     * ProcedureScheduler queues.
     */
    public static void wakeEvents(AbstractProcedureScheduler scheduler, ProcedureEvent... events) {
        scheduler.wakeEvents(events);
    }

    /**
     * Only to be used by ProcedureScheduler implementations.
     * Reason: To wake up multiple events, locking sequence is
     * schedLock --> synchronized (event)
     * To wake up an event, both schedLock() and synchronized(event) are required.
     * The order is schedLock() --> synchronized(event) because when waking up multiple events
     * simultaneously, we keep the scheduler locked until all procedures suspended on these events
     * have been added back to the queue (Maybe it's not required? Evaluate!)
     * To avoid deadlocks, we want to keep the locking order same even when waking up single event.
     * That's why, {@link #wake(AbstractProcedureScheduler)} above uses the same code path as used
     * when waking up multiple events.
     * Access should remain package-private.
     */
    synchronized void wakeInternal(AbstractProcedureScheduler procedureScheduler) {
        if(ready && !suspendedProcedures.isEmpty()) {
            LOG.warn("Found procedures suspended in a ready event! Size=" + suspendedProcedures.size());
        }
        ready = true;
        if(LOG.isTraceEnabled()) {
            LOG.trace("Unsuspend " + toString());
        }
        // wakeProcedure adds to the front of queue, so we start from last in the
        // waitQueue' queue, so that the procedure which was added first goes in the front for
        // the scheduler queue.
        procedureScheduler.addFront(suspendedProcedures.descendingIterator());
        suspendedProcedures.clear();
    }

    /**
     * Access to suspendedProcedures is 'synchronized' on this object, but it's fine to return it
     * here for tests.
     */
    @VisibleForTesting
    public ProcedureDeque getSuspendedProcedures() {
        return suspendedProcedures;
    }

    @Override
    public String toString() {
        return getClass().getSimpleName() + " for " + object + ", ready=" + isReady() + ", " + suspendedProcedures;
    }
}
